Allow attaching text threads as context (#29947)

Release Notes:

- N/A

---------

Co-authored-by: Michael Sloan <mgsloan@gmail.com>

crates/agent/src/thread_store.rs

@@ -58,6 +58,8 @@ impl SharedProjectContext {
     }
 }
 
+pub type TextThreadStore = assistant_context_editor::ContextStore;
+
 pub struct ThreadStore {
     project: Entity<Project>,
     tools: Entity<ToolWorkingSet>,
@@ -361,6 +363,10 @@ impl ThreadStore {
         self.threads.len()
     }
 
+    pub fn unordered_threads(&self) -> impl Iterator<Item = &SerializedThreadMetadata> {
+        self.threads.iter()
+    }
+
     pub fn reverse_chronological_threads(&self) -> Vec<SerializedThreadMetadata> {
         let mut threads = self.threads.iter().cloned().collect::<Vec<_>>();
         threads.sort_unstable_by_key(|thread| std::cmp::Reverse(thread.updated_at));